Replicating sharp broken glass edges
A quick example

To make glass just model it to how u want it to look, try and keep it as random as u can. 


Then just add a glass material 
https://www.youtube.com/watch?v=yRRN7yzPNQI
btw your glass should look way better if u follow the tutorial i just added the material without doing anything to it in the photo below


Also if u dont want to use cycles u can just turn down the transparency (alpha) as ive done here https://sketchfab.com/models/177e494fdada4b64b02acf041ae8cfdd


Edit: Something like this?